This invention relates to an acceleration-slippage controller for controlling acceleration slippage that occurs between a driven wheel and a road surface during acceleration of an automobile.
Prior to this invention, various acceleration-slippage controllers have been introduced. One of them is disclosed in Japanese Published Unexamined Patent Application No. S61-1543, in which, when acceleration slippage of a driven wheel is detected based on a revolution speed of the driven wheel, a driving torque of the driven wheel is controlled until the slippage disappears.
The acceleration-slippage controller of this type maximizes a frictional force between the driven wheel and a road surface during acceleration of an automobile and produces a greater acceleration of the automobile. When a change rate of the revolution speed of the driven wheel exceeds a preset value, or when the revolution speed of the driven wheel exceeds a reference speed determined based on a body speed, it is determined that slippage has occurred.
This determination of slippage occurrence has a problem. If the driver kicks down the acceleration pedal and the automobile accelerates very sharply on the dry road, the revolution speed of the driven wheel greatly increases in a short time. In this case, because the change rate of the driven-wheel speed is very high, the slippage is erroneously detected, resulting in the unnecessary execution of an acceleration-slippage control. This hinders the desired acceleration of the automobile.
The erroneous slippage determination is caused not only by the quick acceleration but by mechanical play in the transmission system. The revolution speed sensor for the driven wheel is normally placed on the output shaft of the transmission. Therefore, when the engine accelerates, the output shaft quickly responds, which makes the slippage determination due to a play of the transmission system. But the driven wheels do not actually accelerate.